1. Field of the Invention
The present invention relates to a heat process device.
2. Description of the Related Art
The course of manufacturing semiconductor integrated circuits includes a baking process for heating semiconductor substrates after photo-resist film is applied to them or photo-resist film coated on them is exposed and developed. One of the heat process devices employed at the baking process is disclosed in preliminarily-publicated Japanese Patent Application No. 58-21332. This heat process device is directed to a semiconductor substrate under heat treatment on a heating plate or heat transfer plate for a predetermined time period at a certain temperature, while heating the heat transfer plate by a heating element or a heater housed in a heating substrate or a plate-like insulater. A heat process is thus applied to the photo-resist film on the semiconductor substrate.
This heat process device, however, has the following drawbacks.
The heating element for heating the heat transfer plate comprises arranging and sealing an electric resistance wire in a plate-like insulator or a heating substrate. The arrangement of the electric resistance wire is not uniform in relation to a heat source for heating of the heat transfer plate in this case. Therefore, the heat flux perpendicular to the surface of the heating plate becomes larger as the object heating point comes nearer to the electric resistance wire. When the heat transfer plate of a smaller width is heated by this SCATERED heat flux, temperature distribution on its surface does not become uniform. In order to uniformly apply heat process to the photo-resist film on the semiconductor substrate, therefore, it is required that the heat flux at the surface of the heat transfer plate is made uniform. This requires the heat transfer plate to be made thick so that the diffusion distance of heat can be made so long as to make the heat flux at the surface of the heating plate uniform. The surface temperature of the heat transfer plate can be thus made uniform.
When the heat transfer plate is made thick, however, the heat capacity of the heat transfer plate is increased and this makes it difficult to quickly raise and lower the surface temperature of the heat transfer plate. When the temperature of the thick heat transfer plate is to be raised, for example, it takes a long time until the surface of the heat transfer plate reaches a predetermined temperature after current is applied to the heat transfer plate. When higher current is added to the heat transfer plate to shorten the time during which the surface of the heat transfer plate is heated to the predetermined temperature, the heating temperature becomes too high to heat the heat transfer plate, that is, there is an over shoot in temperature. When the heat transfer plate which is made thick is to be cooled, the cooling of the heat transfer plate cannot be finished in a practical time period. In order to let the heat process device have a high heat process capacity, therefore, it is required that the heat transfer plate be made large-sized. This also makes the whole device large-sized and heavy.
Further, the heating element and the heating plate or the heat transfer plate are different parts, and indirectly contact via a very small gap. In general, there is a certain amount of the thermal contact resistance between them. The speed of transmitting heat from the heating element to the heating element depends greatly upon the thermal contact resistance of them at the time of assembly. As the result, heating capacity is different for every heat process device thus made. When the heat source is complicated in its structure, breaking of the resistance wire as well as inferior insulation may be caused, thereby lowering the reliability of the devices thus made.